Electroluminescent display panels



May 11, 1965 w. BROOKS ELECTROLUMINESCENT DISPLAY PANELS Filed NOV. 9, 1962 Iv INVENTOR. 2 WILLIAM BROOKS BY f Agent United States Patent 3,182,415 ELECTROLUMINESCENT DlSPLAY PANELS William Brooks, Sunnyvale, Calif., assignor to Lockheed Aircraft Corporation, Burbank, (Ialif.

Filed Nov. 9, 1962, Ser. No. 23%,538 1 (Jlaim. (Cl. 40-430) This invention relates to electroluminescent display panels, and more particularly to electroluminescent display panels having associated therewith replaceable alphanumeric symbols which are responsive to an applied alternating current voltage.

In the prior art, numerous arrangements have been proposed to provide an illuminated panel having alphanumeric and other symbols therein for purposes of display. In general, such illuminated display panels have included a glass face plate or transparent insulative support member having a first semi-transparent conductive coating on one side thereof, a layer of electroluminescent phosphor covering the first semi-transparent conductive coating, and a second conductive coating covering the phosphor layer. The phosphor glows when an alternating current voltage is applied between the first and second conductive coatings to provide light issuing through the glass face plate. In addition, such devices are usually provided with associated engr ied displays which are illuminated by the light issuing through the glass face plate when the engraved display is disposed in the path of the light. In the alternative, the markings or alpha-numeric symbols which are to be illuminated may be formed directly on the exposed surface of the glass in a variety of colors different from that of the phosphor to be illuminated. The phosphor may also act as a background to thereby provide a contrast for ready observation of the display.

Another well known form of display panel in the prior art has a front surface defined by a layer of opaque material, a layer of white translucent material covered by the opaque layer, with the exception of those areas where the white translucent area is exposed through openings in the opaque area, defining the desired markings, or symbols, a relatively thick sheet or layer of clear acrylic material which may be dyed a specific color and carry fluorescent dyes to control color of the emitted light and which is disposed in back of the white translucent layer, a black plate of relatively rigid insulating material which may be also of an acrylic plastic and has recesses in its front face corresponding to the areas of the opaque front layer having alpha-numeric markings defining openings therein, and relatively small electroluminescent plates loosely received in the recesses of the black plate so that when the various plastic sheets and layers are bonded together and voltages applied to the several electroluminescent plates, the latter uniformly illuminate all the alphanumeric symbols defining openings.

It has been found that the aforesaid prior art devices are not readily adaptable to a wide variety of uses. More particularly, in such applications where it is desirable to have a large electroluminescent display panel of a permanent nature, such as an airline schedule board or an ofiice building directory, for examples, with removable alphanumeric symbols, the foregoing prior art devices are incapable ofproviding such features, inasmuch as the alphanumeric markings which are associated with the display panel are usually made a permanent part thereof or re quire the replacement of the entire message to be displayed by the panel. In addition, the symbols are not of conductive material so as to be compatible with an electroluminescent device. Thus, it can readily be seen that prior art devices are incapable of providing an arrangement whereby the alpha-numeric symbols or markings may be changed at will to thereby provide greater versatility where such versatility is required.

The present invention obviates the disadvantages and shortcomings of such prior art display panels by providing a unique and different approach to the display of conventional alpha-numeric symbols. More specifically, the present invention provides an electroluminescent display panel having a transparent support member or face plate with a transparent conductive coating on one side thereof, a layer of electroluminescent phosphor over the transparent conductive coating, a counter electrode, and a plurality of flexible, replaceable alpha-numeric symbols sandwiched between the exposed surface of the electroluminescent phosphor layer and the counter conductive electrode. The surface of the alpha-numeric symbols, which is in contact with the electroluminescent phosphor, causes the electroluminescent phosphor in the area in contact with the symbols to be illuminated when an alternating current voltage is applied between the transparent conductive coating and the counter electrode in such a manner that light issues through the transparent insulative support member.

Accordingly, it is the broad objective of this invention to provide an improved electroluminescent display panel which is adapted for readily changing the individual symbols of a display.

Another object of the invention is to provide an electroluminescent display panel in which a plurality of interchangeable alpha-numeric symbols are utilized to provide greater versatility and for ready reading in the use of the display panel.

Still another object of the invention is to provide an electroluminescent display panel having a plurality of flexible conductive alpha-numeric symbols which make uniform contact with the electroluminescent phosphor to thereby illuminate only the area in contact with the conductive symbol.

Yet another object of the invention is to provide an electroluminescent display panel having a plurality of replaceable alpha-numeric symbols which is economical, silmple, and capable of providing a wide variety of disp ays.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of construction and operation, together with further objects and advantages thereof, will be better understood with the following description considered in connection with the accompanying drawing in which illustrative embodiment of the invention is displayed by way of example. It is expressly understood, however, that the drawing is for purposes of illustration and description only and does not define limitations within the invention.

In the drawing:

FIGURE 1 is a diagrammatic view of an electroluminescent display panel illustrating the use of alphabetical letters in a display device according to the invention.

FIGURE 2 is a fragmentary cross-sectional view of the display panel shown in FIGURE 1 taken along lines 2-2 illustrating the cross-sectional details of the construction of the device and arrangement of the panel in accordance with the invention. I With reference to the drawing, FIGURE 1 shows a section of a display panel 10 which has a plurality of conductive, flexible alphabetical letters 12 which extend along the length thereof to form a display message and to provide an illuminated presentation of the alphabets which is transmitted to a viewer through an insulative front panel 14. In addition, there is shown a clamping member 16 which is provided to hold the conductive alphabets in electrical contact between the associated bols.

being disposed. over the exposed surface of the trans-' parent conductive coating 18, a plurality of alphabetical letters 12 sandwiched between the phosphor20 and a counter electrode 22 which forms the second conductive element for the device for the application of an applied voltage. In FIGURE 2 there is shown three sections in which an alphabetical symbol makes intimate contact between the phosphor layer 29 and the counter electrode 22, thereby defining the area which is illuminated when 'an alternating current voltage is applied between electrodes 18 and 22. The voltage supply for the device is symbolically shown and designated by reference numeral 26. No special voltage supply is required and may be one of several types commercially available.

In operation, the voltage supply 26 is raised to or set at a predetermined voltage level wherebyan electric field produced by the circuitcurrent will. cause the electroluminescent phosphor to be excited. Illumination of the phosphor is restricted to theregion adjacent the alphanumeric symbols such as 24 shown in FIGURE 2 of they present embodiment, thereby defining the areas from which light issues through the panel face plate 14. The light issuing from the panel 10 is communicated to a viewer, symbolically illustrated by a human eye 28 shown in FIGURE 2. i

It should be noted. atthis point that the sharpness of the displayed image issuing from the phosphor adjacent the alpha-numeric symbol is a function of the phosphor utilized and the cross-section configuration of the alphanumeric symbols employed. More particularly, it has been found that the use of a phosphor having a relatively high light versus voltagecharacteristic will provide an unusually clear display. Such a phosphor as that disclosed in the commonly assigned copending patent application Serial Number 191,882, filed May 2, 1962, entitled Improved Electroluminescent Phosphor and Method for Making Same, by William Brooks, has been found to provide suchiresults. In a similar manner, satisfactory results have been obtained by mould ing the alpha-numeric symbols from a resin loaded with graphite or metal particles to make the symbols conductive. A preferred material suitable for this purpose is Conductive Resin No. 1200, produced and available from (:homerics, Inc, at 341 Vassar Street, Cambridge 39, Massachusetts. The alpha-numeric. symbols may be formed by spreading the conductive resin material in a preselected mold form to produce athickness of about which has been found satisfactory. It should be noted that the thickness has not been found to becritical and will depend upon the particular phosphor and the magnitude of the voltage applied thereto. It is desirable to have the surfaces of the phosphor and symbols in total contact with one another. to insure efficient current flow therebet-ween. Thus, it has been found advantageous to employ a compressible material for the sym- In closing, it is useful to summarize some of the advantages of the present invention. One such advantage involves the use of a unique light output electroluminesdesignated 24, of the letter E, illustrating the manner cent phosphor having a rapid light decay versus voltage characteristic which enhances the resolution -or sharpness of the display, since there is little or no light dispersion associated with the illumination of the phosphor in the region adjacent the alpha-numeric symbols.

Another advantage of'the present invention arises from the use of the unique removable and replaceable alphanumeric symbols which may be fabricated economically and easily to provide means for rapidly changing the message to be displayed on a particular panelyand thereby increases the versatility of the display panel. In contrast, the prior art deyices are rather expensive in that theycannot be readily andeconomically modified to accommodate thefmessages displayed thereon without a major modification of the display panel itself.

It is to be understood that the above-described embodiment is only illustrative of the principle applicable in the invention.- Numerous other arrangements and modification may be defined by those skilled in the art without departing from the spirit and scope of the invention. Thus, by way of example, and not limitation, the crosssectional configuration of the alphabet illustrated by sections 24 of the letter E may be made in a configuration other than. a rectangle; that is, the portion adjacent the phosphor may be smaller than the portion adjacent the counter conductor 22, which would provide sufficient area at the back of the letter for good electrical connect 7 tion and would .provide a small area adjacent the phosphor in order to makethe size of the alpha-numeric letter smaller while still providing good electiiecontact with the phosphor. It. should be noted at this point, however, that such an arrangement maynot have all the advantages of the arrangement disclosed in the illustrated embodiment of the present invention. Accordingly, it is to be understood that the present invention is limited only by the spirit and scope of the appended claim.

What is claimed is:

An electroluminescent display .panel comprising: five layers including an insulative transparent support memher, a transpagent conductive layer superimposed on one side-of said support member, a layer of electroluminescent phosphor material superimposed over said conductive layer, and a second conductive layer having a removable symbolic message of conductivematerial sandwiched between said phosphor layer ,and said second conductive layer; clamping means for keeping said symbolic message sandwiched between said phosphor layer and said second conductivelayer; and electrical connection means to said first conductive layer and said second'conductive layer for applying an alternating current voltage thereto for exciting said electroluminescent phosphor layer in regions defined by a conductive symbolic message adjacent thereto which may be viewed by-one facing the unobstructed surface of the transparent support layer,

References tilted by the Examiner UNITED STATES PATENTS JERoMEscnNA LL, PrimaiyEx'tzminerJ All? i 

